As you probably already know, HCC is only applied to records loaded via direct path writes. Any updates cause rows to be migrated out of that storage format into blocks flagged for OLTP compression. Of course OLTP compression on a block only kicks in when a block is “full”. On top of this, altering a table to change it’s compression does not actually change the storage format of any existing records (unless you use the MOVE keyword). So you could load some data and then change the designation (say from QUERY LOW to QUERY HIGH). Rows that are inserted after the change will be stored in the new format (assuming the records are loaded via direct path writes of course). So why am I telling you all this. Well, because I ran across a statement in some Oracle documentation that said you can check to see what compression method a table is stored with by looking at the COMPRESS_FOR column in the DBA_TABLES view. This column does reveal what the table designation is. However, the setting actually only tells you how rows inserted in the future will be compressed. It tells you absolutely nothing about the way current rows are stored.

SO though the table level field could be none there could still be compressed rows in the table...